Summer diet of seabirds from the Frans Josef Land archipelago, Russian Arctic JAN M. WESLAWSKI, LECH STEMPNIEWICZ and KIRYL GALAKTIONOV Weslawski, J . M . , Stempniewicz, L. & Galaktionov, K. 1994: Summer diet of seabirds from the Frans Food samples from 102 seabirds from eight species (fulmar Fulmarus glacialis. common eider Somateria mollissima, glaucous gull Larus hyperboreus, kittiwake Rissa tridoctyla, arctic tern Sterna paradisaea, Briinnichs guillemot Uria lomvia, black guillemot Cepphus grylle, little auk Alle alle) were collected during the period August 1991-1993 in the southern part of the Frans Josef Land archipelago, W N , 53"E. The pelagic amphipod Parathemisto libellula and polar cod Boreogadus saida were the two most commonly taken food items (frequency of occurrence over 50% and weight contribution more than 70%). Ice- associated crustaceans contributed to some 10% of the weight in the samples. In general, the food composition was very similar to that reported from Svalbard. However, birds from Frans Josef Land fed on a lower diversity of prey compared to Svalbard populations. Jan M. Wptawski, Institute of Oceanology, Polish Academy of Sciences, Powstaricdw Warsrawy S.5, 91-967 Sopot, Poland; Lech Stempnie#icz, Department of Vertebrate Ecology and Zoology, University of Gdatisk, Legionow 9, 80-441 Gdarisk, Poland; Kiryl Galaktionov, Murmansk Marine Biological Institute, Russian Academy of Sciences, Vladimirskaja 17, 183023 Murmansk, Russia. n Josef Land archipelago, Russin Arctic. Polar Research 13(2), 173-181. ''*POLAR\NS''. Introduction The Frans Josef Land archipelago belongs to one of the least known areas in the European Arctic with regard to marine ecology. It was only recently that internationally organised expeditions (Russian/Norwegian/Polish) col- lected a sizeable amount of data on the marine mammal, bird and invertebrate fauna of Frans Josef Land (Gjertz & Meirkved 1992, 1993). Seabirds as consumers constitute an important component of the Arctic ecosystem (Croxall 1987). The number of seabirds breeding and feed- ing in the area provides reliable data on marine food supplies which can be used for comparisons between different regions and different years in the same area (Cairns 1987; Furness & Nettleship 1991). In the neighbouring Svalbard archipelago, this topic has been studied by Hartley & Fisher (1936), Lydersen et al. (1989), Stempniewicz & Weslawski (1992), and Mehlum & Gabrielsen (1993). There is a lack of such data from Frans Josef Land, with the exception of old and rather anecdotal reports by Gorbunov (1932), Demme (1934) and Weslawski & Skakuj (1992). The present paper describes the summer diet of seabirds from this area. The paper also presents possible differences between feeding of the same seabird species in two European Arctic regions, Svalbard and Frans Josef Land archipelagoes. The regions are geographically close, but different as to climatic, hydrographic and ecological con- ditions (Weslawski 1993). In general, Svalbard is exposed to the strong influence of the warm West Spitsbergen Current, while Frans Josef Land is situated in the High Arctic zone covered year round with drifting ice. For this reason differences in seabirds feeding are expected. Material and methods During three consecutive summer seasons (August 1991,1992,1993) joint Russian, Norwe- gian and Polish expeditions worked in the area of Hooker Island and the neighbouring islands of the southern-central part of Frans Josef Land archipelago (Fig. 1). Seabirds were col- lected in the vicinity of the colony at Rubini Rock, Hooker Island. The same samples were used for analysis of chemical pollutants and parasites (Matishov 1993) as well as for morphometry and the study of food content. A total of 102 speci- mens from eight seabird species (fulmar Fulmarus glacialis, common eider Somateria mollissima, glaucous gull Larus hyperboreus, kittiwake Rissa tridactyla, arctic tern Sternapardisaea, Briinnich's guillemot Uria lomoia, black guillemot Cepphus 174 Jan M . Wplawski et al. grylle, little auk Alle alle) were examined. All food samples from a given seabird species col- lected in different seasons of the study were pooled because of low sample size. Birds were dissected immediately after being shot. Oesophagus and stomach contents were pre- served in a 4% formaldehyde solution and ana- lysed two months later in the laboratory. In the case of the little auks, the contents of the gular pouches were also used as food samples. Each sample was washed on 0.5 mm mesh size screen and analysed under stereo microscope. The material was sorted and then identified t o the lowest possible taxonomic level. The number, length and weight of all identifiable food items were noted. Standard deviation was calculated only for mean length values of the most numerous food items. In instances where only fragments of prey items were found (fish otoliths, polychaete jaws, crustacean rostra, etc.), the original lengths and weights were calculated from the formulas presented by Berestovskij et al. (1989), Brad- street (1980), and Lydersen et al. (1989). The number of fish and polychaetes ingested was esti- mated as half the number of otoliths and jaws found in the samples. Calorific values of fresh, not fragmented specimens of all prey taxa were measured according to the method described in Szaniawska & Wolowicz (1986). The following coefficients were used to present the results of the analyses of the food samples. Frequency of occurrence (F%) was determined Fig. 1. Sketch map of the study area. The dashed area shows the mean summer ice pack range. The black dot indicates sampling locality. for each bird species as percent number of samples (stomachs) containing given prey type. Also the mean number of a given food item per sample (numerical abundance) and percentage by number, weight and energy of particular prey taxa were calculated. Cluster analyses were performed using the PRIMER programme (Carr 1993) (Plymouth Marine Laboratory, UK) and the Bray-Curtis index of similarity, based on the frequency of occurrence matrix. Empty stomachs and those containing single food item were excluded. Results Food content Fulmar F. glacialis. - Remains of four prey taxa were identified in the food samples. Polar cod Boreogadus saida was the largest prey item (140 mm), and pelagic polychaetes were most numerous. Fish (B. saida and sculpin M y o x o - cephalus spp.) constituted about 85% of food weight. Remains of macrophytes and plastic debris were found in each stomach. N o ice-associ- ated crustaceans were identified in the fulmar diet. (Table 1). Common eider S . mollissima. - Seven prey taxa were found. All stomachs contained gastropods (Margarites helicinus), constituting about 84% of the items and more than 55% of the food weight. Summer diet of seabirds 175 Table I . Stomach contents of five seabird species and food items characterisitics. Mean Mean Total Frequency of Seabird species and length wet weight number of occurrence prey items (mm) (mg) individuals F% by number by weight Percentage Percentage Fulmaris glacialis (n = 5) Polychaeta spp. Margarites spp. Boreogadus saida Myoxocephalus scorpius Pisces n.det. terrestrial plants macrophytes plastic debris Somateria mollissima (n = 5 ) Polychaeta spp. Margarires spp. Onisimus spp. Gammarellus homari Gammarus setosus Weyprechtia pinguis Boreogadus saida Larus hyperboreus (n = 5 ) Boreogadus saida Pisces n.det. birds remains gravel Sterna paradisaea (n = 5 ) Polychaeta (pelagic) Apherusa glacialis Gammarus setosus Gammarellus homari Gammarus wilkitzkii Pisces n.det. Cepphus grylle (n = 5 ) Atylrrs carinatus Gammarellus homari Onisimus spp. Gammarus wilkitzkii Parathemisto libellula Lebbeus polaris Boreogadus saida Myoxocephalus scorpus Pisces n.det. gravel 60 10 141 60 50 5 10 5 60 10 10 30 25 15 162 1 80 50 100 10 60 10 25 30 25 60 30 25 15 15 12 60 140 60 60 200 491 7,589 5,220 1 ,000 4 20 20 200 491 14 511 207 43 11,087 11,ooo 1 ,OOo 50,oOO 100 200 5 207 511 206 1 ,ooo 250 250 50 150 25 800 7.500 1 ,ooo 1 .OOo 3 1 1 1 1 1 2 1 1 31 1 1 1 1 1 2 2 5 1 1 1 3 5 2 1 1 1 1 2 1 4 8 2 2 1 60 27.3 20 9.1 20 9.1 20 9.1 20 9.1 20 9.1 40 18.2 20 9.1 20 2.7 100 83.8 20 2.7 20 2.7 20 2.7 20 2.7 20 2.7 40 20.0 40 20.0 100 50.0 20 10.0 20 7.7 20 7.7 60 23.1 100 38.5 40 15.4 20 7.7 20 4.3 20 4.3 20 4.3 40 8.7 20 4.3 40 17.4 80 34.8 20 8.7 20 8.7 20 4.3 4.0 3.3 50.7 34.9 6.7 0.0 0.3 0.1 0.7 55.8 0.1 1.9 0.8 0.2 40.6 8.0 0.7 91.2 0.0 4.2 0.1 12.9 53.3 8.6 20.9 0.4 0.4 0.1 0.4 0.0 4.7 88.1 2.9 2.9 0.0 Benthic amphipods (Gammarellus homari, Gam- marus setosus, Weyprechtia pinguis, Onisimus spp.) were the second in importance. Ice-associ- ated crustaceans were not present in the food samples (Table 1). Glaucous gull L. hyperboreus. - Remains of juv- enile birds were found in each stomach. They included Brunnich’s guillemots, kittiwakes and little auks. Large polar cods (18 cm) were found in two stomachs. Birds contributed to more than 90% of the energy intake (Table 1). Kittiwake R. tridactyla. - Eight prey taxa were found. The largest prey found was a 16 cm polar cod B. saida, and the smallest was a 4 m m long Culanus glacialis. The most common food items were Amphipoda (apherusa glacialis - 46% and Parathemisto libellula - 32% of all items). Polar cod of mean length 13 cm was the most important food component. It constituted about 90% of food weight and energy intake. Ice-associated crustaceans contributed to only 4% of energy intake (Table 2). Ta bl e 2. S to m ac h co nt en ts in t he K itt iw ak e R is sa m 'd nc ry lo ( n = 1 9) a nd f oo d ite m s ch ar ac te ri st ic s. M ea n (S D) M ea n T ot al E ne rg et ic Fr eq ue nc y of M ea n le ng th w et w ei gh t nu m be r of va lu e oc cu rr en ce nu m be r of P er ce nt ag e Pe rc en ta ge Pe rc en ta ge Pr ey i te m (m m ) ( w ) in di vi du al s (k J/ gd w ) F % in di vi du al s by n um be r by w ei gh t by e ne rg y P ol yc ha et a S Q Q . (p el ag ic ) C al an us S Q Q . A p h ew a g la ci al is G am m ar us W if ki tz K ii Pa ra th em is to l ib el lu la M eg an yc tip ha ne s no rv eg ic a B or eo ga du s sa id a M yo xo ce ph aa lu s sc or pi us te rr es tr ia l p la nt s m ac ro ph yt es 60 .0 (-) 25 .0 (-) 7. 0 (1 .0 9) 6. 4 (1 .3 5) 10 .8 ( 2. 14 ) 13 3. 1 (1 9. 90 ) 30 .0 (-) 60 .0 (- ) 5. 0 (-) 10 .0 (-) 20 0 7 2 20 7 13 27 0 5 . ooo 5, 22 0 4 20 5 19 .7 43 26 .0 29 7 19 .7 55 16 .0 20 8 16 .7 4 22 .0 30 24 .2 1 22 .0 1 1 19 .7 16 16 22 16 84 16 58 5 5 5 0. 5 3. 9 27 .0 5. 0 18 .9 0. 4 2. 7 0. 1 0. 1 0. 1 0. 8 6. 7 46 .0 8. 5 32 .2 0. 6 4. 7 0. 2 0. 2 0. 2 Ta bl e 3 . St om ac h co nt en ts in th e B ru nn ic h' s G ui lle m ot U ri a lo m ui a (n = 1 1) a nd f oo d it em s ch ar ac te ri st ic s. 0. 4 0. 3 0. 1 0. 1 0. 3 0. 1 5. 0 3. 9 1. 6 0. 9 0. 5 0. 4 89 .8 92 .1 2. 3 2. 1 0. 0 0. 0 0. 0 Pr ey i te m M ea n (S D) M ea n To ta l E ne rg et ic Fr eq ue nc y of M ea n le ng th w et w ei gh t nu m be r of va lu e O cc ur re nc e nu mb er o f P er ce nt ag e Pe rc en ta ge Pe rc en ta ge (-) (m g) in di vi du al s (k J/ g dw ) F% in di vi du al s by n um be r by w ei gh t by e ne rg y Po ly ch ae ta S Q P . ( pe la gi c O ni si m us S Q Q . R ha ch ot ro pi s ac ul ea ta G a m m a m w ilk itz ki i G am m an cr s et os us Pa ra th em is to l ib el lu la Th ys an oe ss a in er m is B or eo ga du s sa id a Pi sc es n .d et . gr av el 60 .0 (-) 10 .0 (-) 25 .0 (-) 25 .0 (-) 8. 0 (-) 14 .5 ( 2. 43 ) 15 0. 7 (2 1. 86 ) 25 .0 (-) 50 .0 (-) 10 .0 (-) 20 0 14 8 20 7 20 7 48 15 6 10 ,O oo 1 , O oo 10 0 2 2 1 9 3 15 6 28 22 2 2 18 .0 18 .0 16 .0 16 .0 16 .0 16 .7 22 .0 24 .2 24 .2 18 0. 2 18 0. 2 9 0. 1 54 0. 8 18 0. 3 92 14 .2 9 2. 5 54 2. 0 18 0. 2 18 0. 2 0. 9 0. 9 0. 4 4. 0 1. 3 68 .7 12 .3 9. 7 0. 9 0. 9 0. 2 0. 0 0. 0 0. 8 0. 3 3. 0 1. 9 92 .8 0. 9 0. 1 0. 1 0. 0 0. 0 0. 6 0. 2 1. 7 1. 4 94 .9 0. 9 0. 0 3 3 - s g c w g 5 k p " Summer diet of seabirds 177 Arctic tern Sterna paradisaea. - Six food taxa were identified. An unidentified fish of ca. 10 cm length was the largest prey item. Gammarid crus- taceans ( G . homari, G . setosus, Gammarus wil- kitzkii) were the most numerous and contributed to more than 70% of the food weight. Nearly 10% of the food mass was formed by ice-associated crustaceans (Table 1). Briinnich's guillemot Uria lomvia. - Nine prey taxa were found. The smallest was an 8 mm long amphipod (Rhachtropis aculeata) and the largest was 16cm long polar cod. P. libellula was the most numerous prey constituting about 69% of the items. Polar cod was the main food item both as to weight (93%) and energy value (95%). Ice- associated crustaceans were of negigible import- ance and constituted less than 1% of prey weight and energy (Table 3). Black guillemot Cepphus grylle. -Eight food taxa were identified. Polar cod (16cm long) was the largest prey item. Fish were most important, both in number (nearly 45% of items), and in food weight (90%). Decapods and gammarids contri- buted to less than 10% of the food intake (Table 1). Little auk Alle alle. - Thirteen prey taxa were identified (Table 4). The largest food item was the snail fish Liparis spp. of ca. 60mm length found in one stomach only. The smallest items were 3 mm long Ostracoda. The most numerous taxon was C. glacialis represented both by sub- adult (copepodit IV and V) and adult specimens of 6 to 8 mm long. They constituted 84% of the total number of prey items, and 72% of the food weight. The second most important prey was Thy- sanoessa inermis (about 11% of weight and energy value). Ice-associated Amphipoda (A. glacialis and G . wilkitzkii) contributed to more than 12% of energy intake, while 73% was provided by copepods (Table 4). Food selection and competition Some distinct differences in the size class dis- tribution of most common zooplankters occurring in Frans Josef Land surface waters (Koszteyn & Kwaceniewski 1992) and in the collected food samples were found. The largest specimens of C. glacialis (6-10 mm), the middle sized specimens of P. libellula and the lower mean fraction of A . glacialis were chosen by feeding seabirds. In general, only food items 6 mm long or bigger were selected. Smaller preys constituted less than 7% of total number of items ingested by birds studied. 178 Jan M . Wgsiawski et al. 10 BRAY - CURTIS SIMlLARlTY -L 8 8 8 2 8 8 g g s s o 1 : : : : : : : : : 1 I Fig. 3. Length frequency of all prey items taken by the Black guillemot 1 Brunnich’s Glaucous gull Fig. 2. The dietary overlap-cluster of prey similarity Cluster analysis of seabird diet similarity shows closely related diets of the kittiwake, Briinnich’s and black guillemots, all relied mainly o n polar cod and P. libellula. It appears also that on Frans Josef Land eiders and arctic terns exploit similar food resources (gammarid Amphipods). The little auks took mainly Calanus (70% of food weight and energy) and were separated from other sea- birds as well as the glaucous gulls occupying the distant niche of carnivore and scavenger (Fig. 2). Among the three most numerous seabirds com- pared, the little auks took the smallest, kittiwakes the medium sized, and Briinnich’s guillemots the largest prey items (Fig. 3; Tables 3, 4). In our study seabirds utilising similar food resources (large dietary overlap) preferred different length classes of the same prey. Because of small samples only size of the most common prey items of the kittiwakes and Briinnich’s guillemots (a pair of species with considerable dietary overlap) were compared. Briinnich’s guillemots took signifi- cantly larger polar cods (t = 3.02, df = 50, P < 0.005) and P. libellula (t = 15.60, df = 362, P < 0.001) than the kittiwakes. Polar cod was the only prey item used by nearly all investigated birds. It contributed t o more than 90% of energy intake in the diets of four most numerous seabirds. P. libellula was second of importance with regard to the frequency of occur- length classes In (mm) 60 80 110 140 170 % 0 2 4 6 8 I 0 12 14 16 18 20 22 24 26 28 30 Little auk 10 - 0 2 4 6 8 I 0 12 14 16 18 20 22 24 26 28 30 60 80 110 140170 Frans Josef Land. Summer diet of seabirds 179 them use a wide food range, like the glaucous gull feeding on marine invertebrates, fish, eggs, birds, carrion and offal, in varying proportions depend- ing on local and seasonal availability (Stempnie- wicz & Weslawski 1992). Eiders are less opportunistic and feed on benthic amphipods and thin-shelled gastropods throughout their dis- tribution area in the European Arctic, but usually take locally abundant species of preys (Hartley & Fisher 1936; Uspenskij 1979; Lydersen et al. 1989; Mehlum 1989). Food specialists such as the little auk, use a very narrow feeding niche limited basically to zooplankton. However, even the little auk diet may vary considerably in different areas and seasons. In spring their diet consists mainly of calanoid copepods while in August they take first of all amphipods (Parathemisto sp., A. gla- cialis) and the polar cod (Bradstreet & Cross 1982; Lydersen et al. 1989; Mehlum & Gabrielsen 1993). The relatively low diversity of High Arctic pel- agic ecosystems results in somewhat artificial simi- larity of seabird diet in different arctic regions. The polar cod and P. libellula, the most important food components of Frans Josef Land seabirds, are also reported as main food preys in Svalbard (Lydersen et al. 1989; Mehlum & Gabrielsen 1993) and in the Canadian Arctic (Bradstreet 1980). Some differences in seabird diets in the two, geographically very close areas (Frans Josef Land and Svalbard) may be a result of some distinct differences between these areas concerning cli- mate and hydrology, which influence the com- position of the marine fauna. Pack ice arrives scarcely in the Svalbard waters during the summer and stays far from the western coast where the majority of seabird colonies are situated. In Frans Josef Land waters pack ice is present throughout the year. The coastal ice-covered waters of Frans Josef Land are apparently rich in pelagic crus- tacean resources, contributed t o by sympagic fauna (estimated by Gulliksen & Lonne 1991 to 1-10 g/m3), neritic plankton (decapoda larvae, amphipods - 0.5g/m3; own data) and marine plankton (copepods - l g / m 3 ; own data). Ice- associated fauna contributed to some 20% of seabirds' food in Frans Josef Land. Mehlum & Gabrielsen (1993) report a similar number for ice covered waters in the northern Barents Sea. In the Canadian Arctic, close t o the fast ice edge, sympagic species contribute to ca. 10% of seabirds' diet (Bradstreet & Cross 1982). rence in birds stomachs, but did not contribute significantly to the total energy consumption. Discussion Optimal foraging theory (Stephens & Krebs 1986) predicts minimising foraging costs (in case of sea- birds the costs of flights to feeding grounds, prey location, choice, pursuit, etc.), and maximising energy gains (energy income as a result of feeding). During the breeding period the seabirds should therefore exploit the feeding grounds situ- ated close to colony, offering abundant prey, easy to locate and catch. To obtain more energy during one feeding trip the birds would have to choose sites with high available prey density and food items of maximal size in relation t o their carrying capacity. The longer the distance between the colony and the feeding grounds the bigger food loaJ is more profitable (Croxall 1987). Larger prey taxa (B. saida, G. wilkitzkii, P. inermis) usually constituted the higher proportion of summer diets of the same seabirds in Frans Josef Land (Tables 2, 3, 4) than in Svalbard (Mehlum & Gabrielsen 1993). In addition. selecting bigger prey species within the same genera (C. glacialis versus C . finmarchicus, and P . libellula versus T. abyssorum; Weslawski & Skakuj 1992) could result in larger average size of food items in Frans Josef Land seabirds. How- ever, consideFable. local and seasonal variability in diets demonstrated by Mehlum & Gabrielsen (1993) for Svalbard seabirds as well as small sample size in this study make the above state- ment uncertain. O n the other hand however, mean individual size of P. libellula taken by Frans Josef Land seabirds was smaller compared to Svalbard (Mehlum & Gabrielsen 1993). That may reflect the peripheral character of P. libellula population in West Spitsbergen, where adult, large size classes are more frequent. In Frans Josef Land, at the centre of population occurrence (Koszteyn et al. in press) more even size frequency may be observed, so more accessible and common are middle sized individuals. No differences were found in mean size of polar cod taken by seabirds from Svalbard and Frans Josef Land. That may indicate similar distribution of class sizes in polar cod populations in both areas compared. Seabirds are opportunistic within the food spec- trum they are morphologically, physiologically and behaviourally adapted to exploit. Some of 180 Jan M. Wgsiawski et al. The number of food taxa (zooplankton and fish) recorded in the summer diets of seabirds is considerably lower in Frans Josef Land than at Svalbard. In total, the same three most numerous seabird species (little auk, Briinnich’s guillemot and kittiwake) take 19 prey taxa in Frans Josef Land and at least 36 in Svalbard waters. Ten species of fish were found in the food samples from Svalbard and only three from Frans Josef Land. The latter did not contain representatives of such important groups of marine invertebrates as Gastropods, Cephalopods, Decapods and Chaetognaths (Hartley & Fisher 1936; Mehlum & Gabrielsen 1993; this study). Lower sample size in this study may partly be responsible for that. Compared to the study by Dernme (1934) on Frans Josef Land seabirds of the same species, our data are stikingly different. Demme (1934) recorded very few polar cod and no Parathemisto, but she found the hyperbenthic gammarid Atylus carinatus as predominating in the food sample collection of over 150 seabirds from Hooker Island. Difference in methods (not described in Demme’s paper) might be partly responsible for this discrepancy, otherwise the interpretation is difficult. We may consider all common, subsurface living animals of 5 to 200 mm length as potential prey taxa for seabirds. There are at least 50 such species in Svalbard waters and no more than 30 in Frans Josef Land (Wesiawski et al. 1994), so one might expect a larger overlap in diet and increased inter- specific competition among seabirds in Frans Josef Land. In the situation common on Frans Josef Land, however, when the potential prey is brought up to the surface, pushed into shallow shore water, closely associated with ice, etc., i.e. it aggregates in a natural or extorted way in the sites easily accessible for birds, different seabird species can then feed on the same food resources. This does not involve an increase of the inter- specific competition because food resources are usually superabundant in such places. In other words different seabirds exploit the same feeding niche despite that normally they separate their feeding grounds by zones (e.g. inshore feeding black guillemot and offshore feeding Briinnich’s guillemot) or by layers (e.g. surface feeding kit- tiwake, subsurface feeding little auk and bottom feeding black guillemot). Patchy distribution of zooplankton in the sea makes location of prey aggregations by feeding indication which the birds can perceive, making location easier. The presence of pack ice may be one such indicator (the sympagic fauna constitutes about 20% of the diet). Birds may use pack ice as an aid in finding at least one fifth of their food. The remaining prey can also be found in such places, which are not, however, closely associated with ice floes. Franz Josef Land is situated further north and east than Svalbard and pack ice occurs there permanently in the sounds between the islands throughout the year. During the breeding season seabirds can find abundant and easily available food close to the colony. Our observations show that the majority of seabirds nesting on Rubini Rock forage in the Mellenius Sound, i.e. a few km from the colony. The specific hydrological situation in the sounds (strong tidal currents, upwellings, whirl-pools, etc.) concentrate the food and favour the seabirds feeding there. For instance, mass presence of half-dead pelagic invertebrates pushed by tidal currents into the shallow water along the shore-line was very often observed during our field work. They were exploited extensively by the kittiwakes. In west- ern Spitsbergen however, the large colonies are often situated in the fjords (Norderhaug et al. 1977) and seabirds usually fly some tens of km to their feeding grounds in the open sea. Acknowledgemenu. - We would like to thank our colleagues from Russian/Norwegian/Polish expeditions to Frans Josef Land 1990-1992 for their help during field work. We are obliged especially to Prof. G. G. Matishov, Director of Murmansk Marine Biology Institute, and to Dr Thor Larsen from Norweg- ian Polar Institute, who made the expeditions possible. A. Szaniawska kindly measured calorific values of all prey taxa. Thanks also to Plymouth Marine Laboratory who generously offered to our project the PRIMER package. Financial support was received from the University of Gdadsk (grant nr. BW/ 1140-5-00872). References Berestovskij, G . , Anisimov. A , , Denisenko, C. G., Luppov, E. H . , Savinov, V. S. & Timofeev, S. M. 1989: Pp. 1-23 in: Relationships between size and body mass of some inuert- ebrates and jishes of North-West Atlantic. Akademja Nauk SSSR, Apatity. (in Russian). Bradstreet, M. S. W. 1980: Thick-billed murres and black guillemots in the Barrow Strait area, N.W.T.. during spring: diets and food availability along ice edges. Can. 1. 2001. 58, 2120-2140. Bradstreet, M. S. W. & Cross, W. 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